Tropical Storm IRWIN

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TROPICAL STORM IRWIN DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 AM PDT SAT AUG 27 2005
 
THE CIRCULATION CENTER OF TROPICAL STORM IRWIN HAS BECOME RATHER
DIFFICULT TO LOCATE THIS EVENING...REMAINING PARTIALLY EXPOSED TO
THE NORTHEAST OF THE WEAKENING DEEP CONVECTION. A BLEND OF DVORAK
SATELLITE CLASSIFICATIONS GIVES AN INITIAL INTENSITY OF 40 KT FOR
THIS ADVISORY. DYNAMICAL MODELS...INCLUDING THE GFS-BASED
SHIPS...SUGGEST A GRADUAL INCREASE IN SOUTHEASTERLY SHEAR BEYOND
DAY 2. SINCE THE SEA SURFACE TEMPERATURES ARE EXPECTED TO REMAIN
RELATIVELY WARM THROUGH THE FORECAST PERIOD...THE SHEAR APPEARS TO
BE THE PRIMARY INHIBITOR FOR FURTHER INTENSIFICATION. THE
CANADIAN/UKMET AND ECMWF EVEN INDICATE DISSIPATION IN 48 HOURS. THE
OFFICIAL INTENSITY FORECAST CALLS FOR LITTLE CHANGE OVER THE NEXT 2
DAYS...TAKING INTO ACCOUNT POSSIBLE INTERMITTENT BURSTS OF
CONVECTION NEAR THE CENTER...THEN A GRADUAL WEAKENING THROUGH THE
REMAINDER OF THE PERIOD. HOWEVER...THE FORECAST COULD BE GENEROUS
CONSIDERING THE AFOREMENTIONED DISSIPATION SCENARIO.
 
THE INITIAL MOTION IS ESTIMATED AT 270/9. AN EAST TO WEST ORIENTED
MID-LEVEL RIDGE TO THE NORTH OF THE TROPICAL CYCLONE SHOULD KEEP
IRWIN ON A GENERALLY WESTWARD TRACK.  THE OFFICIAL FORECAST FOLLOWS
THE CONU CONSENSUS AND THE PREVIOUS ADVISORY THROUGH 72
HOURS...THEN CONTINUES WESTWARD AS A SHALLOW SYSTEM WITHIN THE
LOW-LEVEL FLOW.
 
 
 
FORECASTER ROBERTS/KNABB
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0900Z 17.5N 111.9W    40 KT
 12HR VT     27/1800Z 17.5N 113.3W    40 KT
 24HR VT     28/0600Z 17.5N 115.2W    40 KT
 36HR VT     28/1800Z 17.5N 116.8W    40 KT
 48HR VT     29/0600Z 17.5N 118.5W    40 KT
 72HR VT     30/0600Z 17.5N 122.0W    35 KT
 96HR VT     31/0600Z 17.5N 125.5W    25 KT...DISSIPATING
120HR VT     01/0600Z 17.5N 129.0W    20 KT...REMNANT LOW
 
 
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